The invention relates to a method for producing an electromagnetic actuator including an armature driven by two electromagnets against two oppositely acting springs.
An electromagnetic actuator for operating a gas exchange valve in an internal combustion engine is known from the DE 196 31 909 A1. The previously known actuator comprises two electromagnets arranged at a spacing distance relative to each other, and an armature that is operatively connected with the gas exchange valve, and that is movable back and forth between the electromagnets due to magnetic force, against the force of a spring arrangement of two mutually counteracting springs. The actuator further comprises adjusting means, with which the idle or resting position of the armature, that is to say the position of the armature with unenergized current-less electromagnets, is adjusted to the geometric center between the two end positions of the armature. In this context it is found to be disadvantageous, that the resting position can become shifted during the operation, so that after several hours of operation, a readjustment of the resting position is necessary.
From the DE 199 27 823, which is not previously published, an electromagnetic actuator of the initially mentioned type is known, in which the pre-tensioning of the springs is adjusted in such a manner, so that the same energy is stored in the springs due to the compression of the springs resulting from the armature motion.
It is the object underlying the invention to specify a method producing an electromagnetic actuator, which enables an adjustment of the pre-tension of the springs that is durable and optimal for the operation of the actuator.
The above objects have been achieved according to the invention in a method of producing an electromagnetic actuator with the following special features.
According to the invention, an electromagnetic actuator, which comprises two electromagnets arranged at a spacing distance relative to one another, and an armature that is movable back and forth between the electromagnets against the force of two oppositely acting springs, is placed into operation in two successive method steps. In the first method step, the springs are respectively compressed by a certain compression value in repeating compression cycles, so often until the energy, which is stored therein due to their compression, no longer or only insignificantly differs from the energy stored in the respective spring in a preceding compression cycle. Then, in a subsequent method step, an adjustment of the pre-tension of the one spring or of both springs is carried out.
Preferably, the compression value is selected to be equal to the value by which the springs are compressed during the specified operation of the actuator.
The goal of the first method step is to achieve and recognize, as much as possible, a complete setting or settling of the springs and parts of the actuator that move together with the armature. In this context, by the term setting or settling of the springs and of the moved parts of the actuator, one understands a change of the pre-tension of the springs or of the dimensions of the moved parts of the actuator, which results from the operationally caused relaxation phenomena or manifestations in the material structure or grain of the springs and the utilized components. The first method step thus leads to a stationary operating condition, in which the spring characteristics no longer change or only insignificantly change with an increasing number of compression cycles, that is to say with an increasing number of operating hours. Due to the adjustment of the pre-tension of one of the two springs or of both springs, which is carried out only in the subsequent method step, one achieves that setting or settling effects no longer play any role in the following operation and thus also do not make a readjustment of the pre-tension of the one spring or of both springs necessary.
Preferably, the energy stored in the respective spring is determined in that the course of the spring force of the spring that results during the compression of this spring is detected and integrated over the path length or distance corresponding to the compression.
In an advantageous embodiment of the method, the pre-tension of the one spring or of both springs is adjusted in such a manner so that the same energy is stored in both springs due to their compression resulting from the armature motion.
Hereby one achieves that the armature, if it is released from its two end positions and oscillates freely, approaches equally close to the respective oppositely located end positions. As a result of this, the influence of production-caused tolerances of the components, especially of the springs, on the oscillating behavior of the armature is reduced. Additionally, the total energy requirement of the actuator is optimized, because both electromagnets comprise the same current requirement due to the armature approaching equally close thereto. Namely, if the armature, during free oscillation, would approach closer to the one electromagnet than the other, then the current requirement of the one electromagnet would be reduced by a certain amount, whereas, however, the current requirement of the other electromagnet would increase by a multiple of this amount, so that also the total energy requirement of the actuator would increase relative to the optimal value.